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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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GLACIATION OF THE YAKUTAT BAY BEGION                221
leys whose mouths are not submerged. Calahonda valley, for example, hangs about 600 feet above eastern Disenchantment Bay, minus the slight amount to 'which its rock lip, now buried by outwash gravels, lies below sea level. The Aquadulce valley, at the native sealing camp, probably hangs more than 900 feet. Several small valleys on the west side of lower Russell Fiord hang one or two hundred feet above sea level, but their total discordance to the bottom of Russell Fiord is 1000 or 1200 feet. The visible 700 foot discordance of a prominent hanging valley in Nunatak Fiord is increased to over 1300 feet by the depth of 612 to 666 feet of water in the fiord.
It is impossible to state how much Turner Glacier hangs above the bottom of Disenchantment Bay, for soundings are lacking here. Turner is much smaller than Hubbard Glacier and the discordance should be great. The visible discordance is at least four or five hundred feet, to which the nearest sounding adds only 276 feet. Between this sounding and the Turner Glacier, however, is just where the powerful Hubbard Glacier should have eroded most deeply within the steep walls of Disenchantment Bay, and we should be surprised if the water is not over 900 or 1000 feet deep in that part of the fiord.
Submerged Glacial Deposits. The soundings in the fiords tributary to Yakutat Bay add to our knowledge of the glacial deposits below sea level. It is unfortunate that time was not available for determining the material on the bottom of the fiord and for taking
FlG. 19.    LONGITTJDINAL SECTION OB1   NUNA.TAK FlOBD AND GLACIER.    VmETIOAL AND  HORIZONTAL SCALEB
THHI Sturm.
temperatures, etc., and, in the absence of bottom samples, little can be said of the specific nature of the submerged glacial deposits. We can speak more definitely, however, of the topography of some of the underwater deposits.
In Nunatak Fiord the soundings reveal a shoal a little less than 1J miles from the 1910 ice front (Fig. 19). Upon this the water is 261 feet deep in mid fiord so that the shoal rises 294 feet above the fiord bottom to the east (toward the glacier) and about the same amount above the more distant deep region to the west. This may be either a moraine or a rock ridge. The ice front stood here as recently as 1899 but we do not know for how long. We had previously suspected a shoal here, for large icebergs habitually stranded upon it, especially near the north shore, in 1905 and 1909. It may be morainic, as Fig. 19 suggests. It is of undetermined width and descends most steeply on the east side (suggesting an ice contact), where the slope is not less than 800 feet to the mile, and probably much less steeply on the west where the slope is between 100 and 200 feet to the mile and flattens to 84 feet to the mile and less in a short distance where there may be stratified deposits built by former streams from the ice and by fiord currents. As the glacier is known not to have halted very long at this 1899 position we regard it as possible that the submerged moraine is built upon a slight irregularity of the fiord bottom, due to differential glacial erosion; but we do not know enough of the relative resistance to glacial erosion by the rocks making the fiord bottom to determine this, and it is considered possible rather than probable.
A second shoal which may be wholly or in part a submarine moraine is at the junction